Field of the Invention
The disclosure generally relates to method and apparatus for building a three-dimensional MEMS element with buckled elements. More particularly, the disclosure relates to methods and articles of manufactures that use a film's internal stresses to produce out-of-plane 3D microstructures.
Description of Related Art
The field of three-dimensional micro-electro-mechanical systems (3D MEMS) is still at its infancy. Despite efforts aimed at developing new MEMS manufacturing processes for creating 3D microstructures, conventional fabrication techniques (e.g., surface and bulk micro-machining, CMOS) are still largely two dimensional. The features produced by these techniques are defined predominantly on the wafer plane with very limited possibility of creating functional elements that extend in the out-of-wafer-plane dimension.
Consequently, most MEMS devices are still comprised of planar, 2D elements and are therefore intrinsically limited in their ability to provide three-dimensional functionalities such as sensing and actuation. This has resulted in highly tailored solutions where multiple MEMS units with different detection modes and sensitivity are combined to allow multi-axial functionalities. Aside from increasing manufacturing cost, the approach has increased device complexity.
In an effort to overcome these limitations, some fabrication techniques have been recently developed that provide non-trivial heights in MEMS. For example, deep reactive ion etching (DRIE) is a technology that enables creating very high aspect-ratio elements (i.e., wafer-scale). DRIE has been widely adopted over the past decade. However, DRIE does not yield fully three-dimensional elements, as it does not make curved surfaces. Instead, DRIE results in quasi 3D elements that are created by etching (i.e., projecting) 2D geometries into a substrate. Additional approaches to high aspect ratio microstructures include LIGA and gray scale lithography. These techniques present similar limitations to DRIE and are typically more costly than DRIE.
To date, polymer MEMS is the only field where fully 3D elements have been realized. Microstereolithography of thick polymeric layers (e.g., SU-8 photoresist) has attracted particular attention, in which several groups have demonstrated complex geometries such as micro-turbines, micro-gear and helicoid cogs. In addition to microstereolithography, interference lithography allows rapid fabrication of large-area, periodic 3D templates on sub-micrometer polymeric substrates, with accurate control of both element symmetry and volume fraction. However, even these approaches are not suited for applications where high strength and limited structural deformability are required (e.g., actuators and shock sensors). This is due to the fact that polymers are typically characterized by very low Young's moduli (e.g., ESU8˜3-4 GPa while ESilicon˜130 GPa).
High temperature applications are also incompatible with polymer technologies. The practicality of polymer-based 3D MEMS is therefore limited and dependent on the selected application, hence requiring alternative processes to create fully three-dimensional MEMS element using material such as silicon and metals.
Therefore, there is a need for a method and system for developing an on-chip 3D polymer MEMS that overcome the above-described shortcomings.